West Nile effected any bird that eats carrion; hawks, owls, crows, vultures, etc. These are red winged blackbirds, grackles, etc; SEED eating birds, not bug eaters or carrion eaters. Birds can be effected by the unlikeliest things. For example, if you have a bird in your house, you should know NOT to cook on teflonware in the same room as a bird. I don't know what it is that is released but it is supposedly toxic to birds, yet humans, pet dogs, cats, lizards, and even fish are NOT effected by it.
The way I see it, either a bunch of crops or areas in which these birds forage have been poisoned, either intentionally or unintentionally. (Perhaps where our newly planed crops for the coming year will be planted
) OR, something has been released in the air or upper atmosphere, however, if an air contaminant, other birds (hawks, owls, ravens, nuthatches, warblers) would be effected as well. The more I think of it, judging by the species reports I've seen, it's more than likely something that the birds ate on seed sources. The fish kills could be coincidental or perhaps from watershed and run-off into waterways.